To assess whether the reduced integrin activation, we observed in ICU patients with COVID-19 was due to epitope masking by von Willebrand factor or other multimeric proteins, we compared the agonist-induced PAC-1 binding of 3 severe patients and 3 controls in diluted whole blood, platelet-rich plasma, or after platelet isolation. The gene discussed is VWF; the disease is COVID-19.